This invention relates to novel heat-developable photosensitive materials, and more particularly, to novel heat-developable photosensitive materials having high sensitivity and improved image density and exhibiting less fog upon heat development.
Heat developable photosensitive materials and their image forming processes are well known in the art and described in the literature, inter alia, "Fundamentals of Photographic Engineering --Non-Silver Salt Photography--", Corona Publishing K.K., Tokyo, Japan (1982), pages 242-255; "Image Information", Apr. 1978, page 40; and Nebletts Handbook of Photography and Reprography, 7th ed., Van Nostrand Reinhold Company, pages 32-33; U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, and 3,457,075; British Pat. Nos. 1,131,108 and 1,167,777; and Research Disclosure, June 1978, pages 9-15 (RD 17029).
A number of methods have been proposed for producing color images through heat development. For example, a process for forming color images through reaction of an oxidant of a developing agent with a coupler is known from U.S. Pat. Nos. 3,531,286, 3,761,270, and 4,021,240, Belgian Pat. No. 802,519, and Research Disclosure, September 1975, pages 31-32.
Formation of a positive color image by a photosensitive silver dye bleaching process is described in, for example, Research Disclosure, April 1976, pages 30-32 (RD-14433), ibid, December 1976, pages 14-15 (RD-15227), and U.S. Pat. No. 4,235,957.
Additionally, a process comprising imagewise releasing a mobile dye by heating and transferring the dye to a dye-fixing layer containing a mordant through a medium such as water, transfer to a dye-fixing material with the aid of a high boiling organic solvent, transfer to a dye-fixing material with the aid of a hydrophilic thermal solvent contained in the dye-fixing material, and transfer of a thermally diffusible or sublimatable mobile dye to a dye receiving material on a support were proposed as disclosed in the following patents:
______________________________________ U.S. Pat. Nos. 4,463,079 4,474,867 4,478,927 4,483,914 4,500,626 4,507,380 Japanese Patent Application Kokai Nos. 58-149046 58-149047 59-152440 59-154445 59-165054 59-168439 59-174832 59-174833 59-174834 59-174835 59-180548 59-218443 ______________________________________
Japanese Patent Application No. 60-79709.
A wide variety of silver halide emulsions are known as useful in heat development.
The silver halide emulsions for heat development are deemed to be of a different design from conventional silver halide emulsions subject to wet processing because heat development proceeds as physical development. Although silver halide emulsions that can form a latent image serving as a physical development nucleus seem useful in this sense, no explicit directions have been determined on the design of silver halide emulsions for heat development.
There have been available no silver halide emulsions for heat development that are characterized by a high sensitivity, a minimized range of sensitivity varying with temperature and humidity during exposure, a minimized range of sensitization or desensitization by pressure, minimized latent image fading, and minimized photographic variation during shelf storage.
In general, the development of heat-developable photosensitive materials employs an auxiliary developing agent which functions to accelerate development as by mediating reaction between silver halide and a primary developing agent. Commonly used examples of the known auxiliary developing agents include hydroquinone, alkyl-substitutued hydroquinones such as t-butylhydroquinone and 2,5-dimethylhydroquinone, catechols, pyrogallols, halogen-substituted hydroquinones such as chlorohydroquinone and dichlorohydroquinone, alkoxy-substituted hydroquinones such as methoxyhydroquinone, and polyhydroxybenzene derivatives such as methylhydroxynaphthalene. Also effective are methyl oleate, ascorbic acid, ascorbic acid derivatives, hydroxylamines such as N, N'-di-(2-ethyoxyethyl)hydroxylamine, pyrazolidones such as 1-phenyl-3-pyrazolidone, 4-methyl-4-hydroxymethyl-1-phenyl-3-pyrazolidone, reductones, and hydroxytetronic acids.
Most of these auxiliary developing agents, however, are not regarded as having a sufficient development accelerating effect. Some auxiliary developing agents suffer from a problem of increasing fog, irrespective of some development accelerating effect.
Besides, heat development often experiences fogging which is unexpectable from the conventional wet development or processing with developing solution. A variety of fog inhibiting techniques have been proposed to control such fogging. For example, although U.S. Pat. No. 3,589,903 described that mercury compounds are effective in suppressing fogging under heat development, the use of the compounds toxic to the human body is undesired. Japanese Patent Application Kokai No. 60-198540 describes certain hydroquinone derivatives and 2,4-disulfonamidephenol derivatives, which are less satisfactory in fog inhibiting effect and tend to desensitize high sensitivity silver halide emulsions.